The main tell that a system is an illegal copy is as NHN said - it is locked to a particular release of VCDS. In our 15 years of operating this business, we have never locked a customer to a version of our software. The people who bought their very first system back in 2000, still enjoy free updates to the latest software! And yes, Customer 1 is still with us! And yes, they have updated hundreds of times over the 15 years for free.
Whenever you see a system that tells you it is VAG-COM or VCDS "XX.XX" you know it to be an illegal copy. Doesn't matter what screws are in the shell. It's the "screws" they put to you that matter!